The special section articles demonstrate the importance of informant discrepancies. They also illustrate challenges posed by discrepancies, plus opportunities for advancing research and practice. This commentary addresses these cross-cutting issues: (a) Discrepancies affect many kinds of assessment besides ratings of children's problems. (b) Symptom models complicate challenges posed by discrepancies. (c) Informant discrepancies validly reflect different genetically and environmentally influenced aspects of children's functioning. (d) Multisource assessment is needed to test and refine diagnostic constructs. (e) Methodological issues arise from the kinds of variables that are rated and ways of evaluating agreement. (f) Assessment requires age-, gender-, informant-, and society-based norms. (g) Developmental levels affect what can be assessed, by whom, in what contexts, and for what purposes. (h) Research-based algorithms are needed for using multi-informant data to assess individuals. (Contains 1 table and 1 figure.)